An inkjet printing system typically includes one or more printheads and their corresponding ink supplies. Each printhead includes an ink inlet that is connected to its ink supply and an array of drop ejectors, each ejector consisting of an ink chamber, an ejecting actuator and an orifice through which droplets of ink are ejected. The ejecting actuator may be one of various types, including a heater that vaporizes some of the ink in the chamber in order to propel a droplet out of the orifice, or a piezoelectric device which changes the wall geometry of the chamber in order to generate a pressure wave that ejects a droplet. The droplets are typically directed toward paper or other recording medium in order to produce an image according to image data that is converted into electronic firing pulses for the drop ejectors as the print medium is moved relative to the printhead.
Motion of the print medium relative to the printhead may consist of keeping the printhead stationary and advancing the print medium past the printhead while the drops are ejected. This architecture is appropriate if the nozzle array on the printhead can address the entire region of interest across the width of the print medium. Such printheads are sometimes called pagewidth printheads.
A second type of printer architecture is the carriage printer, where the printhead nozzle array is somewhat smaller than the extent of the region of interest for printing on the print medium and the printhead is mounted on a carriage. In a carriage printer, the print medium is advanced a given distance along a print medium advance direction and then stopped. While the print medium is stopped, the printhead carriage is moved in a direction that is substantially perpendicular to the print medium advance direction as the drops are ejected from the nozzles. After the carriage has printed a swath of the image while traversing the print medium, the print medium is advanced, the carriage direction of motion is reversed, and the image is formed swath by swath.
The ink supply on a carriage printer can be mounted on the carriage or off the carriage. For the case of ink supplies being mounted on the carriage, the ink tank can be permanently mounted to the printhead, so that the printhead needs to be replaced when the ink is depleted, or the ink tank can be detachably mounted to the printhead, so that only the ink tank itself needs to be replaced when the ink tank is depleted. Carriage mounted ink tanks typically contain only enough ink for up to about several hundred prints. This is because the total mass of the carriage needs be limited, so that accelerations of the carriage at each end of the travel do not result in large forces that can shake the printer back and forth. As a result, users of carriage printers need to replace carriage-mounted ink tanks periodically, depending on their printing usage, typically several times per year.
The cost of an ink tank is related to how much ink it contains. High printing throughput users may prefer high capacity ink tanks, which have a higher selling price, but need to be replaced less frequently. Low printing throughput users may prefer low capacity ink tanks, which have a lower selling price. Ink tank manufacturers want to satisfy the requirements of a wide range of users, so it is advantageous to be able to provide a range of ink fill volumes in the ink tanks.
Providing a range of different ink fill volumes is not as simple as filling an ink reservoir in an ink tank to different levels. The ink tank should be capable of containing the ink even under conditions where the pressure within the tank changes due to environmental conditions. For example, pressure variations within an ink tank can occur due to changes in ambient temperature such as when a tank is stored at elevated temperatures in a warehouse or a particular geographic region where high temperatures are encountered. Pressure variations within an ink tank can also occur when the tank is subjected to changes in barometric pressure such as transporting the tank in an airplane or a geographic elevation high above sea level. Some types of ink tank designs are particularly susceptible to leakage due to pressure variations in the ink tank if there is excessive air in the ink tank. For example, a vented ink tank having a chamber containing free-flowing liquid ink, such as that described in U.S. Pat. No. 5,742,312 and in some of the references cited therein, is more susceptible to such pressure-variation-induced leakage than an ink tank having all of the ink retained within a porous capillary medium. If an ink reservoir in an ink tank is partially filled with free-flowing liquid ink, and the remainder of the ink reservoir volume is occupied by air, pressure variations within the ink tank due to variations in environmental pressure and temperature can become excessive and cause leakage of ink from the ink tank during shipping and storage. This results in both wastage and inconvenience for the user.
One approach that has been commonly used is to provide different geometry ink tanks that have different fill volumes. There are limitations on the amount of change in external dimensions (height, width and length) of an ink tank that can be accommodated in a carriage. For a multi-color inkjet printer, it may be possible to select one ink tank (e.g. for black ink) that is positioned at an outer region of the carriage and change its external dimensions for varying the ink capacity. However, generally the external dimensions of a full set of ink tanks cannot be made much larger or smaller than a standard size and still fit in the carriage.
Another approach is to change the volume of an ink reservoir in an ink tank by modifying the internal dimensions, e.g. by changing the position of internal walls or partitions within the ink tank body. However, each variation in ink capacity requires that a new ink tank body style be separately tooled and injection molded, adding to the cost and complexity of manufacturing.
Similarly, the internal dimensions of an ink reservoir in an ink tank can be modified by changing the size of protrusions that extend into the reservoir from the lid of the ink tank, as disclosed in commonly assigned copending U.S. patent application Ser. No. 12/139,544 filed Jun. 16, 2008. However, again each variation in ink capacity requires that a new ink lid style be separately tooled and injection molded, adding to the cost and complexity of manufacturing.
What is needed is a way of providing a range of ink fill levels in a reservoir of an ink tank, without leaving excessive air in the reservoir, and without requiring a different tank body or lid style for each ink fill level.